1. Field of the Invention
The invention herein relates to the field of chemical processes for the preparation of haloacylamides, particularly haloacetanilides, useful in the agronomic arts, e.g., as pesticides and plant growth regulators.
2. Description of the Prior Art
Haloacylamides and haloacetanilides of the type described herein have been prepared by a variety of means known to the prior art. In one prior art process, described in U.S. Pat. No. 2,863,752 (Re 26,961) N-substituted-2-haloacetanilides are prepared by reacting a primary or secondary amine with the acid chloride of haloacetic acid typically in the presence of caustic soda to neutralize the by-product hydrogen halide. A similar process is described in German OLS 1,903,198 wherein the intermediates and final products are characterized by the N-substituent loweralkoxyethyl wherein the ethyl radical may have one or two methyl groups attached thereto.
In yet another prior art process described in U.S. Pat. No. 3,574,746, N-substituted-N-cycloalkenyl-2-haloacetamides are prepared by the haloacetylation of the corresponding N-substituted-cycloalkylimine in the presence of an acid acceptor.
Still another prior art process for producing 2-haloacetanilides is described in U.S. Pat. Nos. 3,442,945 and 3,547,620 wherein the appropriate intermediate compound, an N-halomethyl-2-haloacetanilide, is reacted with the appropriate alcohol preferably in the presence of an acid binding agent. An analogous process is described in Canadian Patent No. 867,769 wherein fluoroacylamino-trichloromethyl-chloromethane is reacted with a thio compound of the formula Me-S-R where Me is H or alkali metal; when the thio compound is used in the free form it is expedient to use an acid-binding agent; when the thio compounds are used in the form of their salts, it is not necessary to add an acid binding agent.
The processes of each of the above '752, '945 and '620 patents are also described in U.S. Pat. No. 3,875,228 as useful in the preparation of 2-haloacetamides (also described as acylamines) exemplified by N-chloroacetyl-N-substituted (hydrogen, lower alkyl, alkoxymethyl, allyloxymethyl or methoxyethyl)-aminoindanes.
As relevant to the present invention involving the alcoholysis of the N-haloalkyl-N-substituted 2-haloacylamide or 2-haloacetanilide intermediate, the prior art (see, e.g., the above '945, '620 and '228 patents) describes the preparation of the 2-haloacetanilide intermediate by the haloacetylation of the appropriate phenylazomethine. See also U.S. Pat. No. 3,637,847.
In another process described in the Journal of the Chemical Society, Volume 1, pages 2087-88 (1974) by O. O. Orazi et al, N-halo-N-substituted amides and imides are methylenated at the nitrogen-halogen bond using diazomethane to produce the corresponding N-halomethyl-N-substituted-amide or imide followed by condensation with nucleophiles. One species of this process involves the reaction of N-chloro-N-methyl-2-chloroacetamide with diazomethane to produce the corresponding N-chloromethyl-N-methyl-2-chloroacetamide, which can then be reacted with a nucleophile.
In the above-mentioned '746 patent, Examples 57 and 54, respectively, disclose N-chloromethyl and N-bromomethyl-N-substituted-cycloalkenyl-2-haloacetamides which are representative of this class of compounds which can serve as intermediates in the process of the present invention. Still other known processes for producing some intermediates used in this invention involve the N-haloalkylation of the appropriate aniline followed by N-haloacylation. For example, N-2-chloroethyl or N-2-chloro-1-methylethyl 2-haloacetanilides may be prepared by reacting the corresponding aniline with 2-chloroethyl-p-toluene-sulfonate and 2-chloro-1-methylethyl-p-toluene-sulfonate, respectively, followed by chloroacetylation. Still another process for preparing the N-haloalkyl intermediate involves reacting the appropriate haloalkane, e.g., 2-chloro-2-bromoethane, with the appropriate aniline followed by chloroacetylation.
In the process for producing N-substituted-2-haloacetanilides by alcoholysis of the corresponding N-haloalkyl-2-haloacetanilide intermediate compound, hydrogen halide is generated as a by-product which adversely affects not only the yield of desired product, but also adversely affects the natural environment. Hence, as indicated in the above '945, '620 and '228 patents, it is necessary that this alcoholysis be conducted in the presence of an acid-binding agent. Examples of acid-binding agents which have been used in the prior art include inorganic and organic bases such as the alkali metal and alkaline earth metal hydroxides, and carbonates, e.g., sodium and potassium hydroxide, sodium carbonate, etc., tertiary amines, e.g., trimethyl- and triethylamines, pyridine and pyridine bases, ammonia, quaternary ammonium hydroxides and alcoholates; metal alcoholates, e.g., sodium and potassium methylates, ethylates, etc. Both the hydrogen halide and the acid-binding agent can promote adverse side reactions which are undesirable, hence, constitute a disadvantage in prior art processes.
A significant disadvantage commonly encountered in the above-mentioned prior art processes is that the acid-binding agent reacts with the by-product hydrogen halide to form insoluble precipitates which must be separated from the reaction mixture and disposed of. Separation of the desired product from waste by-products frequently requires and/or includes stripping of any solvent used, aqueous washing, steam stripping of hydrogen halide, dehydration, filtration and/or stabilization of product. Other purification procedures include fractional distillation at sub or super atmospheric pressure, solvent extraction, film distillation, recrystallization, etc. For example, it is disclosed in Example 4 of each of the above '945 and '620 patents that in the production of N-(butoxymethyl)-2'-t-butyl-6'-methyl-2-chloroacetanilide (common name "terbuchlor"), the acid-binding agent, i.e., triethylamine, forms a voluminous precipitate of fine needles of triethylamine hydrochloride which must be removed by aqueous washing, solvent stripping and filtration. The same problem is also described in the above-mentioned '746 patent (see Column 6, lines 18-33).
As another example, when ammonia is used as the acid-binding agent in the production of 2',6'-diethyl-N-(methoxymethyl)-2-chloroacetanilide (common name "alachlor" and active ingredient in the commercial herbicide LASSO.RTM., registered trademark of Monsanto Company), ammonium chloride is formed as a solid by-product in large quantity and must be disposed of.
In some instances, during or after the alcoholysis of the N-haloalkyl intermediate, the bulk of the generated hydrogen halide by-product can be removed by conventional distillation. However, the hydrogen halide itself is a gaseous pollutant in the environment. Moreover, in some cases distillation of the reactant alcohol and by-product hydrogen halide results in the production of an alkyl halide and water and water is detrimental to yield of product. Further, a certain percentage of the hydrogen halide remains in the reaction mixture and must be removed by an acid-binding agent, thus forming solid waste products as mentioned earlier. For example, in prior work on the alachlor process by another worker in the laboratories of applicants' assignee herein, efforts were made to remove by-product HCl with excess methanol by conventional vacuum distillation. However, these efforts involved prolonged exposure, i.e., .about.2 hours, of the N-chloromethyl intermediate and final product (alachlor) to the adverse action of HCl, water and other by-products and resulted in greatly diminished yields of alachlor. It was then concluded that for optimum yield an acid-binding agent should be used during or after the distillation stage, hence encountering the attendant disadvantages mentioned above.
In view of energy conservation and environmental considerations bearing on the disposal of process wastes it has become exceedingly crucial to find new processes which eliminate or minimize the adverse impact of all kinds of wastes, i.e., solids, liquids and/or gases from chemical processing. In some instances deleterious by-products can be reprocessed for recycling of component parts. In other situations, by-products may be purified or converted to other useful products. However, each of the foregoing treatments require additional capital investment and reprocessing costs and energy consumption. Accordingly, it is much more desirable to avoid the creation of environmentally adverse products as far as possible.
Still another problem in connection with known prior art processes for the production of 2-haloacetanilides is that they are batch processes with attendant disadvantages, particularly on a commercial scale.
Therefore, it is an object of this invention to provide an improved process for producing 2-haloacylamides or 2-haloacetanilides which overcomes disadvantages of prior art processes. In particular it is an object of this invention to provide the advantages of a process which requires no acid-binding agent and produces substantially no solid wastes thereby eliminating some raw material, equipment and separation costs and solid waste disposal problems inimical to the environment.
Still other objects of this invention relate to a process which is continuous, simple and inexpensive in operation, conserves energy, reduces environmental pollution and yet produces yields and purities as great or greater than prior art processes.